This invention relates to the treatment of relatively small volumes of waste water of a high biological oxygen demand so that the waste water permissibly can be discharged into a natural flowing stream or the like, and wherein the system therefor is readily transportable from site to site.
Transportable waste water treatment systems for the removal of entrained hydrocarbon gases from waste water have been employed in specific situations, such as in the degassing of gasoline contained in a pond of water or the like. These systems function by moving large volumes of air through a downwardly flowing stream of the gas/water mixture so that the gas vapors are entrained in the flowing air and swept from the mixture. There is no conversion or degradation of the hydrocarbons in these systems.
U.S. Pat. No. 4,351,729 discloses a technique directed to the anaerobic bacterial conversion of organic pollutants to mainly carbon dioxide and methane. To this end, in accordance with this patent, the waste water is flowed downwardly through a packing material contained in a sealed vessel, the packing material carrying an anaerobic bacteria biomass. Air and other sources of molecular oxygen are excluded from the vessel. Carbon dioxide and methane produced by the reaction within the vessel or from external sources flow upwardly through the biomass on the packing material to be eventually exhausted from the top end of the vessel. The system of this patent is useful only for an anaerobic bacterial conversion process. The liquid effluent ("outfall") from the vessel is stated to be suitable infeed to an aerobic digester.
U.S. Pat. No. 5,674,399 discloses a sewage treatment system and method which employs a settling tank containing an activated sludge plus a submerged biofilm filter. The tank is filled with a batch of liquid sewage. This liquid is continuously circulated through the biofilm filter and the settling tank until the batch has been treated sufficiently t permit its disposal. Upon completion of a treatment cycle, a portion of the liquid is removed from the tank, leaving a portion of the liquid and the activated sludge in the tank. The activated sludge and the biofilm are sources of microbes for digesting each batch of sewage which is admitted to the tank. If the flow rate of the incoming sewage is low enough, this system can be operated as a continuous system, but only at low throughput rates. Disruption of the activated sludge and its microbial population are be avoided, so that the movement of the liquid into the tank initially, and during recirculation of the liquid through the biofilm filter are to be carefully controlled. This feature places a limit on the usefulness of this and similar systems.
Other biological degradation systems include the use of lagoons where the waste water is allowed to remain in the presence of bacteria for long periods of time. These systems require inordinate times and volumes of stored waste water, hence are costly. Moreover, in these systems, the waste water must be transported to the lagoon site.
Digesters are another system which has been employed in the degradation of organics in waste water. These systems generally comprise a submerged biomass through which waste water is repeatedly recycled to effect aerobic treatment of the waste water. Basically, a digester is a form of lagoon in which the waste water is recycled. The digester merely concentrates the biomass into a smaller volume.
It is an object of the present invention to provide a compact transportable system for reducing the biological oxygen demand (BOD) of waste water to a permissible level for ready disposal of the waste water. Under certain circumstances, it is another object to provide a compact fixed system of the type described. Another object is to provide for reduction of the chemical oxygen demand (COD) of waste water, either in combination with, or in addition to, the reduction of biological oxygen demand of the waste water.
Another object is to provide a method by which the biological oxygen demand of waste water is reduced to a permissible level for ready disposal of the waste water.